Network with several subnetworks

ABSTRACT

The invention relates to a network with several subnetworks, which are organized either decentrally or centrally and can be connected in each case each by bridge terminals, a proxy terminal for a bridge terminal being set up in at least one of the subnetworks, which proxy terminal during an absence (dictated by frequency, time, code, or other factors) of the bridge terminal accepts all data directed to the bridge terminal or to be forwarded thereby, temporarily stores the data, and forwards said data to the bridge terminal when this is present again.

The invention relates to a network with several subnetworks, eachconnectable by bridge terminals.

The subnetworks may operate at different frequencies or codes or atdifferent times. Within each individual network, terminals communicatein a wireless manner over one or more radio sections. Furthermore, acentral monitoring station may or may not be present within asubnetwork.

Such a network is known for example from “Habetha, J.; Nadler, M.:Concept of a Centralised Multihop Ad Hoc Network; Proceedings EuropeanWireless, Dresden, September 2000”. In this known network, adjoiningsubnetworks operate at different frequencies and are linked together bybridge terminals that are in the overlap range of two subnetworks. Thebridge terminals take part alternately in the operation within the twosubnetworks, by switching back and forth from one frequency to theother. There is the possibility in each of the subnetworks ofsuppressing any transmission to the bridge terminal while it isoperating at the frequency of another subnetwork. This is managed by acentral monitoring station in each of the subnetworks, which isresponsible for the assignment of transmission resources within thesubnetwork and is informed about the absence of the bridge terminal.During the absence of the bridge terminal, the central monitoringstation thus allocates no transmission capacity to any other stationswhich have applied for a transmission directed at the bridge terminal.

It is an object of the invention to provide a network with improvedcommunication possibilities between the subnetworks. The object isreached according to the invention with a network with several networks,each connectable by bridge terminals, wherein it is provided that in atleast one of the subnetworks a proxy terminal for a bridge terminal isset up, which during an absence of the bridge terminal accepts datadirected to the bridge terminal or to be forwarded by the bridgeterminal, temporarily stores the data, and forwards said data to thebridge terminal when this is present again.

According to the invention, a bridge terminal therefore chooses adifferent station as its proxy, which accepts and temporarily stores alldata directed at the bridge terminal during the absence of the bridgeterminal. When the bridge terminal switches back to the frequency (thecode or time range) of the subnetwork under consideration, the proxythen passes to the bridge terminal all the data accepted on its behalfin the preceding period.

The present invention relates advantageously to a network in which in atleast one subnetwork either no central monitoring station exists or forsome other reason a transmission to the bridge terminal cannot besuppressed during its absence.

The object is also reached according to the invention with a bridgeterminal according to claim 5 and a proxy terminal according to claim 6.

The networks may be organized either decentrally or centrally.

The absence may be dictated by frequency, time, code or other factors.

If a central monitoring station exists in a subnetwork, but atransmission to the bridge terminal is not possible during its absence,the central monitoring station is chosen by the bridge terminal as itsproxy, according to a preferred embodiment of the invention.

The invention will be described in more detail below with reference toembodiments shown in the drawings, in which:

FIG. 1 shows an ad hoc network with three subnetworks, each containingterminals provided for radio transmission, FIG. 2 shows a terminal ofthe local network as in FIG. 1, FIG. 3 shows a radio device of theterminal as in FIG. 2, and FIG. 4 shows an implementation of a bridgeterminal provided for connecting two subnetworks, and the proxy terminalof this bridge terminal.

The embodiment presented in the following relates to ad hoc networks,which in contrast to traditional networks are self-organizing. Everyterminal in such an ad hoc network can enable access to a fixed networkand can be used immediately. An ad hoc network is characterized in thatthe structure and the number of participants are not fixed withinpredefined limiting values. For example, a communication device of aparticipant can be taken out of the network or linked in. In contrast totraditional mobile telecommunication networks, an ad hoc network is notdependent on a permanently installed infrastructure.

The size of the ad hoc network's area is generally very much greaterthan the transmission range of a terminal. A communication between twoterminals can therefore necessitate the activation of further terminals,so that these can transfer messages or data between the twocommunicating terminals. Such ad hoc networks, in which forwarding ofmessages and data via a terminal is necessary, are referred to asmultihop ad hoc networks. Multihop ad hoc networks can either beoperated at a frequency (or a code or time range), or consist ofsub-networks that each operate at a different frequency, code or timerang. A subnetwork of the ad hoc network may be formed, for example, byterminals, connected over radio links, of participants sitting round atable. Such terminals may be, for example, communication devices forwireless exchange of documents, images, etc.

Two types of ad hoc networks can be specified. These are decentralizedand centralized ad hoc networks. In a decentralized ad hoc network, thecommunication between the terminals is decentralized, i.e. each terminalcan communicate directly with any other, provided that the terminal iswithin the other terminal's transmission range in each case. Theadvantage of a decentralized ad hoc network is its simplicity androbustness against errors. In a centralized ad hoc network certainfunctions, such as the function of multiple access of a terminal to theradio transmission medium (Medium Access Control=MAC), are controlled byone particular terminal per subnetwork. This terminal is referred to asthe central terminal or central controller (Central Controller=CC).These functions need not always be executed by the same terminal: theycan be transferred from one terminal serving as the central controllerto another terminal then acting as central controller. The advantage ofa central ad hoc network is that an agreement on the quality of service(QoS) is easily possible in it. One example of a centralized ad hocnetwork is a network that is organized according to the HIPERLAN/2 HomeEnvironment Extension (HEE) (see J. Habetha, A.Hettich, J. Peetz, Y. Du,“Central Controller Handover Procedure for ETSI-BRAN HIPERLAN/2 Ad HocNetworks and Clustering with Quality of Service Guarantees”, 1^(st) IEEEAnnual Workshop on Mobile Ad Hoc Networking & Computing, Aug. 11, 2000).

FIG. 1 shows an embodiment of an ad hoc network with three subnetworks 1to 3, which each contain several terminals 4 to 16. Constituents of thesubnetwork 1 are the terminals 4 to 9, of the subnetwork 2 the terminals4 and 10 to 12, and of subnetwork 3 the terminals 5 and 13 to 16. In asubnetwork, the terminals belonging to that subnetwork exchange dataover radio links. The ellipses drawn in FIG. 1 specify the radiocoverage area of a subnetwork (1 to 3), in which a largely problem-freeradio transmission is possible between the terminals belonging to thesubnetwork.

The terminals 4 and 5 are called bridge terminals, because these enabledata exchange between two subnetworks 1 and 2 or 1 and 3 respectively.The bridge terminal 4 is responsible for the data traffic between thesubnetworks 1 and 2, and the bridge terminal 5 for the data trafficbetween the subnetworks 1 and 3.

A terminal 4 to 16 of the local network according to FIG. 1 can be amobile or a fixed communication device and contains, for example, atleast one station 17, a connection-checking device 18, and a radiodevice 19 with an antenna 20, as shown in FIG. 2. A station 17 may be,for example, a portable computer, telephone, etc.

As is shown in FIG. 3, a radio device 19 of the terminals 6 to 16comprises besides the antenna 20 a radio-frequency circuit 21, a modem22, and a protocol device 23. The protocol device 23 forms packet unitsfrom the data stream received from the connection-checking device 18. Apacket unit contains part of the data stream and additional controlinformation formed by the protocol device 23. The protocol device usesprotocols for the LLC layer (LLC=Logical Link Control) and the MAC layer(MAC=Medium Access Control). The MAC layer controls the multiple accessof a terminal to the radio transmission medium, and the LLC layerperforms a flow and error control.

As was mentioned above, a specific terminal may be responsible for themonitoring and management functions in a subnetwork 1 to 3 of acentralized ad hoc network, and in this case is referred to as a centralcontroller. The controller also works as a normal terminal in theassociated subnetwork. The controller is responsible, for example, forthe registration of terminals that start operations in the subnetwork,for the connection setup between at least two terminals in the radiotransmission medium, for the resource management, and for the accesscontrol in the radio transmission medium. Thus, for example, afterregistering and after signaling a desire to transmit, a terminal in asubnetwork is allocated transmission capacity for data (packet units) bythe controller.

In the ad hoc network, the data may be exchanged between the terminalsby a TDMA, FDMA, CDMA, or CSMA method (TDMA=Time Division MultiplexAccess, FDMA=Frequency Division Multiplex Access, CDMA=Code DivisionMultiplex Access, CSMA=Carrier Sense Multiple Access). The methods mayalso be combined. Each subnetwork 1 to 3 of the local network isassigned a number of specific channels, referred to as channel groups. Achannel is defined by a frequency range, a time range or, for examplewith the CDMA method, by a spreading code. For example, a specificfrequency range, different in each case, with a carrier frequency f₁ maybe available to each subnetwork 1 to 3 for data exchange. In such afrequency range, data can be transferred by TDMA or CSMA, for example.The carrier frequency f₁, may be allocated to the subnetwork 1, thecarrier frequency f₂ to the subnetwork 2 and the carrier frequency f₃ tothe subnetwork 3. The bridge terminal 4 operates on the one hand at thecarrier frequency f₁ in order to be able to execute a data exchange withthe other terminals of subnetwork 1, and on the other hand at thecarrier frequency f₂ in order to be able to execute a data exchange withthe other terminals of subnetwork 2. The second bridge terminal 5included in the local network, which transfers data between thesubnetworks 1 and 3, operates at the carrier frequencies f₁, and f₃.

FIG. 4 is a block diagram of an embodiment of a bridge terminal. Theconstruction of the proxy terminal may also be executed in the same way.The radio switching device for this bridge terminal comprises a protocoldevice 24, a modem 25 and a radio-frequency circuit 26 with antenna 27.The protocol device 24 is connected to a radio switching device 28,which is further connected to a connection-checking device 29 and abuffer memory device 30. The buffer memory device 30 in this embodimentcomprises a storage element, is used for temporary storage of data, andis implemented as a FIFO module (First In First Out), i.e. the data isread from the buffer memory device 30 in the order in which it waswritten into it. The existence of a buffer memory facility for the proxyterminal is of special significance, since this temporarily stores alldata directed to the bridge terminal during its absence. The memory canbe divided into logic areas for separate storage of the data fromdifferent connections. The terminal shown in FIG. 4 can likewise work asa normal terminal. Stations connected to the connection-checking device29, which are not drawn in FIG. 4, then deliver data via theconnection-checking device 29 to the radio switching device 28.

The bridge terminal of FIG. 4 is synchronized alternately with a firstand a second subnetwork. Synchronization is understood to be the entireprocess of integrating a terminal up to the exchange of data. If thebridge terminal is synchronized with the first subnetwork, it canexchange data with the terminals adjacent to it in radio range, and witha controller (if present) of this first subnetwork. If data is deliveredfrom the connection-checking device 29 to the radio switching device 28,its destination being a terminal or the controller of the firstsubnetwork or a terminal or controller of another subnetwork which canbe reached via the first subnetwork, the radio switching device forwardsthis data directly to the protocol device 24. The data is temporarilystored in the protocol device 24 until the time slot determined by thecontroller for the transmission is reached. If the data output from theconnection-checking device 29 is to be sent to a terminal or thecontroller of the second subnetwork or to another subnetwork accessiblevia the second subnetwork, the radio transmission must be delayed untilthe time slot in which the bridge terminal is synchronized with thesecond subnetwork. The radio switching device therefore routes the datawhose destination is in the second subnetwork or accessible via thesecond subnetwork, to the buffer memory device 30, which temporarilystores the data until the bridge terminal is synchronized with thesecond subnetwork.

If data from a terminal or the controller of the first subnetwork isreceived by the bridge terminal, its destination being a terminal or thecontroller of the second subnetwork or a terminal or controller ofanother subnetwork accessible via the second subnetwork, this data islikewise stored in the buffer memory device 30 up to the synchronizationwith the second subnetwork. Data whose destination is a station of thebridge terminal is passed directly via the radio switching device 28 tothe connection-checking device 29, which then routes the received datato the desired station. Data whose destination is neither a station ofthe bridge terminal nor a terminal or controller of the secondsubnetwork is sent, for example, to a further bridge terminal.

After the change of synchronization of the bridge terminal from thefirst to the second subnetwork, the data stored in the buffer memorydevice 30 is read back from the buffer memory device 30 in the order inwhich it was written. Then, during the period of time that the bridgeterminal is synchronized with the second subnetwork, all data whosedestination is a terminal or the controller of the second subnetwork, oranother subnetwork accessible via the second subnetwork, can be passedon at once from the radio switching device 28 to the protocol device 24,and only the data whose destination is a terminal or the controller ofthe first subnetwork, or another subnetwork accessible via the firstsubnetwork, is stored in the buffer memory device 30.

The proxy terminal is constructed similarly to the bridge terminal, butdoes not perform a frequency change. It is informed about its proxy rolein a once-only or periodic explicit signal from the bridge terminal. Theproxy terminal can refuse this role. If it accepts the proxy role, thebridge terminal informs the proxy terminal about the starting time andduration of its absence (or once only about the periods of its presencesand absences).

If during the absence of the bridge terminal data is received from aterminal or a controller of the first subnetwork, its destination beingthe bridge terminal or-a terminal or controller of the second subnetworkaccessible via the bridge terminal, this data is stored in the buffermemory device 30 of the proxy terminal until the return of the bridgeterminal to the first subnetwork. Data whose destination is a station ofthe proxy terminal itself is passed directly via the radio switchingdevice 28 to the connection-checking device 29, which then routes thereceived data to the desired station.

After the return of the bridge terminal, the data stored in the buffermemory device 30 of the proxy terminal is read back from the buffermemory device 30 in the order in which it was written and sent to thebridge terminal. The proxy terminal may either be informed explicitly bya signal from the bridge terminal about its return, or it may infer thereturn time implicitly from the periods of the presence and absencetimes for the bridge terminal. Afterwards, during the period of timethat the bridge terminal is synchronized with the first subnetwork, alldata whose destination is a terminal or a controller of the secondsubnetwork, or another subnetwork accessible via the second subnetwork,can be accepted by the bridge terminal itself.

As an example of a possible embodiment for two adjoining subnetworks,one of the subnetworks could work in accordance with the IEEE Standard802.11, while the second subnetwork to be connected would operate inaccordance with the ETSI Standard HIPERLAN/2. This would presuppose thatthe bridge terminal was able to communicate in accordance with bothstandards. In this case a proxy terminal only has to be set up in thefirst (CSMA-based) subnetwork, which is working in accordance with theIEEE 802.11. In the second HIPERLAN/2 subnetwork, the so-called centralcontroller could suppress all transfers to the bridge terminal duringits absence. As was noted for the general case, according to theinvention, the central monitoring station of the 802.11 network, calledthe “Point Coordinator (PC)” or “Hybrid Coordinator (HC)”, should (ifactive) be selected as the proxy terminal in the 802.11 basedsubnetwork. If no PC/HC is active in the first subnetwork, the bridgeterminal may choose any terminal in this network as the proxy terminal.For example, in this case the best receivable adjoining terminal of thisnetwork could be selected as proxy terminal. The invention is thussuitable for connecting together networks operating in accordance withdifferent standards.

Another embodiment of the invention could, for example, involve thelinking together of two or more subnetworks of the same standard. If twoadjoining subnetworks operate work in accordance with the IEEE 802.11Standard at different frequencies, for example, at least one bridgeterminal and a proxy terminal should be set up in each of the twosubnetworks.

Finally, a further possible arrangement of the proxy concept should bedescribed in which at least two or more bridge terminals are set upbetween the same subnetworks. If the bridge terminals coordinate theirpresence in the adjoining subnetworks in such a way that always at leastone bridge terminal is present (this is suggested, for example, in“Peetz, J.: HiperLAN2 Multihop Ad Hoc Communication byMultiple-Frequency Forwarding, Vehicular Technology Conference, Rhodes,May 2001”), the bridge terminal present any given time the time couldact as the proxy terminal for the other bridge terminals set up betweenthe same subnetworks.

1. A network comprising: several subnetworks, each connectable by bridgeterminals and including at least one other terminal, wherein at leastone of said at least one other terminal provided in at least one of thesubnetworks is set up as a proxy terminal during a planned absence ofone of said at least one of the bridge terminals from said one of thesubnetworks, wherein the proxy terminal accepts designation as a proxyserver by said absent bridge terminal; accepts data directed to saidabsent bridge terminal or to be forwarded by said absent bridge terminalto said one of the subnetworks, temporarily stores the data, andforwards said data to said absent bridge terminal when said absentbridge terminal is present again in said one of the subnetworks, whereinsaid planned absence of said one of said at least one bridge terminalsfrom said one of the subnetworks is for a predetermined time; whereinone or more of the subnetworks includes a central monitoring station,wherein for each subnetwork having a central monitoring station, thecentral monitoring station is selected as the proxy terminal for saidbridge terminal during the planned absence of said bridge terminal. 2.The network of claim 1, wherein at least two subnetworks operate inaccordance with different communication standards, and the bridgeterminals operate in accordance with both communication standards fordata exchange of those subnetworks that operate in accordance withdifferent communication standards.
 3. The network of claim 1, wherein aplurality of bridge terminals connect a same two of the subnetworks andwherein during the absence of one of the plurality of bridge terminals,another one of the plurality of bridge terminals is selected as theproxy terminal.
 4. The network of claim 1, wherein at least two of thesubnetworks connectable by the bridges are wireless subnetworks eachcomprising a plurality of terminals that communicate wirelessly witheach other.
 5. The network of claim 1, wherein at least one subnetworkincludes a central controller, and wherein during the absence of thebridge terminal, the central controller suppresses data transfers to thebridge terminal.
 6. A bridge terminal for a network comprising at leasttwo subnetworks, each of said two subnetworks having a plurality ofterminals, said bridge terminal comprising: an antenna; a radio deviceconnected to the antenna; a protocol device connected to the radiodevice; a radio switching device connected to the protocol device; abuffer memory connected to the radio switching device; and wherein thebridge terminal operates such that when the bridge terminal isunavailable to one of said two subnetworks, the bridge terminal selectsone of the terminals in the one of said two subnetworks to be a proxyterminal and the selected terminal operates to: function as a proxyserver selected by the bridge terminal; receive all data directed to thebridge terminal to be transferred to said one of the two subnetworks,temporarily store the data, and forward the data to the bridge terminalwhen the bridge terminal is again available to the one of the twosubnetworks, wherein the unavailability of the bridge terminal from saidone of the two subnetworks is planned for a predetermined time, whereinwhen the bridge terminal is unavailable to one of the two subnetworks,and when the one of the two subnetwork has a central controller, thenthe bridge terminal selects the central controller to be the proxyserver.
 7. In a network comprising at least first and second subnetworkseach having a plurality of terminals linked by a bridge terminal, aproxy terminal provided in the first subnetwork, the proxy terminalcomprising: an antenna; a radio device connected to the antenna; aprotocol device connected to the radio device; a radio switching deviceconnected to the protocol device; and a buffer memory connected to theradio switching device, wherein the proxy terminal operates such thatwhen the bridge terminal is unavailable to the first subnetwork, theproxy terminal: accepts designation as a proxy server selected by thebridge terminal; receives all data directed to the bridge terminal to betransferred to first network, temporarily stores the data, and forwardsthe data to the bridge terminal, when the bridge terminal is againavailable to the first subnetwork, wherein the unavailability of thebridge terminal from the first network is planned for a predeterminedtime, wherein the proxy terminal designated as the proxy server is acentral controller in the first subnetwork.